In commercial refrigeration units, a condenser is normally located on the roof top where heat can be exhausted to the ambient atmosphere. The output from the condenser then flows to a receiver tank where it is stored and liquid from the receiver tank then flows to expansion valves and an evaporator where cooling occurs as the refrigerant changes phase from liquid to gas. The output from the evaporator then travels by suction to one or more compressors and the output from the compressor then returns to the condenser wherein heat is extracted therefrom and the cycle is repeated.
It is desirable to maximize the subcooling in the condenser so that the refrigerant is cooled below the phase change transition temperature and that subcooling retained to a maximum extent as the liquid recirculates.
It is further desirable to minimize the amount of refrigerant charged to the system and to operate at the lowest possible discharge pressure from the condenser.
However, when the subcooled liquid from the condenser is stored in a receiver, it may be heated. Accordingly, in U.S. Pat. No. 4,831,835, it was proposed to bypass the receiver selectively based upon the output temperature of the condensed liquid from the condenser. When the liquid temperature drops below a predetermined value indicating the desired level of subcooling, the bypass is activated and the subcooled refrigerant flows from the condenser to the expansion valves. When the liquid temperature increases above the desired level, the bypass is closed and flow from the condenser to the receiver is opened. According to the first condition the receiver remains in the flow path through a pressure regulating valve even when bypassed.